Thanks guys!
I'll add one more consideration (variable)
@CarolynFH. Why are you training?
-If you're training for the purpose of getting fit, losing weight, exercise in general, then choosing the time of day with the lowest amount of solar radiation and T+D is ideal. It just makes it more comfortable to run.
-If you'e training for a specific race, then the ideal temperature during the day may not be the best time to train. I personally evaluate my goal race's history to determine what race day weather conditions will be like. I use
Weather Underground. Under the name of the city is a "History" tab that allows you to choose any day from the past several years. In addition, once you choose your historical race day (for instance a race in New Orleans on May 6th) then I would go through the last 5 years of data to determine what the race day conditions are like. Once you choose a historical date, you can scroll downwards to get hour by hour conditions for both temperature and dew point. It's a really nice feature. Use the last 5 years of data to make a reasonable guess range as to what race day will be like.
Like this:
View attachment 219186
I was making a choice between these two races (DoLittle and Lakefront). I was trying to evaluate the historical T+D on the day and time of the race to see whether either had an advantage over the other. Lakefront won easily even though they're only separated by one week (more T+D in the 100 or less).
Once you know what the historical weather is like on race day, that's an important consideration for training. The closer you get to race day the more and more you want to make sure you're training in similar conditions. So if your race is May 6th in New Orleans (made up) and the typical T+D is 155, then when I'm making choices about time of day training for that race and I have morning at 120 and afternoon at 155 I should choose the 155. The body undergoes physiological adaptations to environmental conditions. So training in 155 T+D will make you a better runner at 155 T+D. If you consistently train at 120 T+D and race day is 155 T+D, then race day is likely not to go as well as training would indicate. The currently held scientific understanding is it takes about 14 days or 10 workouts to adapt to a new environmental condition. So the last two weeks before race day become hyper critical to not avoiding the non-ideal T+D if that's what race day will be like.
So the adage I use when training for a specific race is, "You never know what race day will be like, so train in all safe environmental conditions."
Hope this helps!